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Development of occlusion

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Introduction to Orthodontics …

Introduction to Orthodontics
Fifth Year

Published in Health & Medicine , Technology
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  • 1. Development of occlusion 5 phases of the development of occlusion from birth to adult life: 12345- From birth to complete eruption of primary teeth: 2.5 yr. From the completion of primary teeth to the eruption of 6: 2.5-6 yr. Mixed dentition period from the eruption of 6 to the final shedding of primary teeth: 6-12 yr. Permanent dentition period from the eruption of 7: 12 yrs on wards. Dentitional and occlusal development in young adult. Gum pads:                        the alveolar arches at the time of births which are firm and pink. Developing into 2 parts: labiobuccal and lingual portion. The labiobuccal portion is divided by transverse grooves into the segments, each corresponding to a descidious tooth sac. Of these grooves those between the **** & 1st molar segment are important in assessing the relationship of the gum pads to each other, they are called lateral sulci they are the only one to extend to the buccal sides. It is separated from the lingual portion by the dental groove which is site of dental lamina. The lingual portion remains almost entirely smooth. It is limited lingually by the gingival groove. In the upper jaw the gingival groove separate the gum pads from the palate. It defines the limits of palate by 3 almost straight borders  forming part of oblong. The lower gum pad is U-shaped, anteriorly is slightly everted labially. Devided by segments ( but not clear as in upper) The groove distal to the canine is continued in the buccal surface and it is called the lateral sulcus. At the rest the gum pads are separated by the tounge, which protrudes over the lower gum pad to lie behind the loer lip. At this age the upper lip appears too short. The upper gum pad is wider than the lower one, and when they are approximated there is a complete overjet all around of the upper over the lower gum pad with a considerable overjet anteriorly. The lateral sulcus of lower gum pad is usually posterior to that of the upper. It is common to see a vertical space between the upper and lower incisors segments of the gum pads even when they pressed into occlusion. This usually occupied by the tounge and not necessarily leads to anterior open bite. The limits of anterioposterior movement is small and there is no lateral movement. At birth, the gum pads are not sufficiently wide to accommodate the developing incisors, which are crowded and rotated in their crypts. During the first year of life the pads grows rapidly and the growth is marked in the lateral direction. The increase of width permits the incisors to erupt in good alignment and to be spaced. However, in spite of this increase, the incisors may erupt while still in their original irregular relation to each other. This is considered a temporary normal condition which is later corrected by tongue and lip pressure, provided that sufficient supporting bone has been offered by growth.
  • 2. Primary dentition: -formation. -calcification. -Eruption. -Size and shape. -Anomalies -Root resorption -Ankylosis -primary occlusion. -change in occlusion. Formation:   Began about 3 m in I.U life when clefts of the face begins to close. Start as thickening of oral epith -> dental lamina  bud stage  cap stage  bell stage. Calcification:     Start about 4 m in I.U life in incisors area, then one month later in canine and molar area. Calcification start in incisal edge and cusp tips. It appears as small discrete masses that coalesce together forming cusp tip. 14 to 12 of deciduous crown is formed before birth. Eruption:     It is movement of teeth through and within the bone of the jaws and underlying mucosa to appear in the oral cavity and contact the opposing teeth. Emergence: is the 1st sign of appearance in the oral cavity. Dental lamina degenerates, fuse with the oral epithelium forming a tunnel through which tooth move. Theories of eruption: 1- root formation.    2- B.V pressure. 3- pulpal growth pressure. Systemic disturbance with teething: fever, pain….etc. Race Sequence: AB A D BD C C E E
  • 3. Size: Inherited as well as mineral level. M>F (cuspid) UA 6mm, LA 4mm and UE 9.5mm. Anomalies: Rare in deciduous, congenital missing is not frequently seen, supernuemerary in UA may be found. Root resorption: Proceeds eruption of permanent. Hastened by inflammation, careis, trauma delayed by absence of permanent and splinting. Primary teeth eruption chart. ‫صورة‬ Ankylosis: Root of deciduous fused with the alveolar bone. It may be caused by trauma or pressure!! Common in 1ry molar, in mandible than maxilla. Called submerged. Natal teeth: Present at birth. In mandibular Incisor area. Root may be not formed (too mobile) Removed if cause ulceration to the tongue or difficulties in sucking.
  • 4. Development of occlusion of 1ry dentition: 1-incisors are the first teeth to erupt.they erupt more in vertical position and deep overbite which decrease by6 the eruption of molars.  Erupt with generalized space if not leads to crowding 2- the 2ed teeth to erupt are the primary molar, lower is slightly forward to upper. 3-next the canines, there is apace mesial to upper, distal to lower ( anthropoid to primate space) 4-2ed primary molar is the last tooth to erupt, U MP cusp occludes in the buccal groove of lower.  Distal surface of the upper flush with the distal surface of the lower, flush terminal plane. Normal occlusion in the 1ry is characterized by: Spacing between anterior teeth. Spaced mesial to the max. canine and distal to the mand., at which opposing interdigitates. Lower incisal edge touch the cingilum of the upper. Flush terminal plane. Characteristic spacing: Developmental: space between incisors. Primate: maxmesial to the canine Variations of occlusion: No space, crowding. Absence of primate space. Mesial or distal step Increase in overjet Overbite may diffident or deep mand distal to the canine.
  • 5. Change in occlusion(2.5-5.5yr) A. Changes in spacing  Closure of space between D&E  Apparent increase spaces between incisors by attrition. B- Incisor relationship :    Overbite and overjet Decrease Overbite Decrease by : attrition , Growth of the alveolar process , and normal position of incisors . Overjet Decrease by : Forward position of the Mandible , attrition of cusp tips , forward sliding of the mandible and hence ; edge to edge relation. D- Change in Arch dimension :   Slight Increase in Arch Width . Slight Increase in Arch Length .
  • 6. Permanent Dentition     Tooth calcification Eruption : a- Relation ( ) eruption and calcification b- Timing c- Factors affecting timing d- Sequence e- Factors affecting tooth position during eruption f- Anomalies Arch dimensions Development of occlusion -Calcification :  1st tooth is 6 which starts its calcification few weeks after birth .  As calcification of permanent occur after birth , it is subjected to malformation more than Primary.  Females are advanced than males in all stages , race … -Eruption :  During eruption : Root of Deciduous resorb , Root of permanent Lengthen ,and alveolar bone increases in height . A- Relation between eruption and calcification  Teeth not begin to move till crown is completed.  Pass through Alveolar Crest after 2 thirds root formed.  Pierce gingival when 3/4 root is formed.  Root completed few months after occlusion is attained. B- Timing :  Variation up to 12 months could exist .( go back to the table for 1ry and permanat teeth eruption) C-Factors affecting timing of eruption :  Sex  Height and weight : earlier in heavier and taller .  Loss of 1ry teeth … half  Periapicallesions. D- Sequence :  LOWER : 6 1 2 3 4 5 7  UPPER : 6 1 2 4 5 3 7 Eruption of Mand. 3 ahead of 4,5 prevent lingual collapse of incisors , Other :   LOWER : 6 1 2 4 3 5 7 UPPER : 6 1 2 4 3 5 7 Deviation in sequence can lead to arch length problems as : Eruption of 7 ahead of 3,4,5 which will lead to Space deficiencies .
  • 7. E- Factors affecting tooth position during eruption :  Tooth pass through 4 stages during eruption : 1- pre-eruptive genetic . 2- intra-alveolar ( neighboring pathology , loss of decid. , root resorption ) 3- intra oral balance . 4- Occlusal : vertical … canceled , Mesial : ant comp … canceled by lip pressure . F- Anomalies :  Agenesis : Total (anadontia) , Partial (hypodontia) -Absence of Permanent Teeth :  4-6% congenital absence  Females more .  Most common congenitally absent teeth : MAND 2nd premolar , MAX lateral incisor , MAX 2nd premolar . Development of Permanent occlusion : it is divided into 3 stages :    Stage 1 : eruption of 6 and incisors . Stage 2 : eruption of cuspid , bi-cuspids and 2nd molar . Stage 3 : eruption of 3rd molar . -Stage 1 : A- 1st permanent molars : its eruption usually occurs ahead of central incisors , but reverse might occur . it is guided in its position by distal surface of E . proper position of 6 is obtained by : ( forward movement of mandible “early shift” , and late mesial shift ) B- Mandibular incisors : -Centrals – lies and erupt lingual to as causing its exfoliations , moved to its normal position by tongue . -Laterals – its eruption is lingual to its precursors , its eruption  exfoliation of B , distal tipping of C in primate spaces . in crowding cases , loss of C  lingual tipping of incisors . - Transient crowding might occur , spontaneous correction. C- Maxillary incisors : - Erupt in a more labial inclination m greater MD and LL dimensions. Maxillary centrals erupt with distal inclination and midline space which closed partially by eruption of laterals and completely by eruption of canines .
  • 8. -  Maxillary laterals has a fanned pattern in eruption , during early development it presents lingual to central latter , correct itself with growth . - If there is insufficient room  erupt lingual to central . - During development of canine , its crown lies labial and distal to root of laterals erupt in a more labial position to central “ ugly ducking stage “ which is relived by eruption of canines . - Sometimes , minor rotations in incisors , spontaneous correction after canine’s eruption . Incisor Replacement Are 2-3.5 mm wider than primary incisors = incisor liability . Solutions : -Normal spacing : developmental and primate . -Labial positioning of permanent ( maxillary ) incisors increases in arch width across canines , these erupt buccally ( max >mand ; boys > girls ) -Distal repositioning of canines in mandible . incisors force mandibular canines distally into primate space . - increase arch perimeter by eruption with more labial inclination . Central Diastema -closes with eruption of lateral incisors . if not will close with eruption of canines careful – frenulum .  Arch width : Inter canine : in Mandible 1.1mm by distal tipping of 1ry canines in primate spaces with eruption of permanent incisors . In Maxilla 1.7 mm which is associated with active eruption of incisors. Inter premolar : deciduous .      slightly in both arches , might be due to narrower MD width of permanent than Inter molar :Max significantly than mand . which might due to lingual eruption of mand molars in addition , mesial shift . Arch circumference : Mandibular -late mesial shift -Mesial drifting tendency of Post. Teeth -Lingual position of incisors due to differential maxillary mandibular growth Maxillary - Greater labial inclination of incisors . - Greater thickness Arch Length : Less significant , half circumference . Variation from ideal development in stage 1 : variation in spacing / crowding conditions : -it affects laterals more than centrals . 6 might be impacted against distal surface of E . Variation in anteroposteriorrelationship : overjet . overjet .
  • 9.    Variation in vertical relationships : -Deep bite . -Open bite . Variation in lateral relationships : -Cross bite Localized variation in tooth position : - trauma , supernumerary , retained 1ry … etc -Stage 2 :     Includes eruption of 3,4,5 and 7 Mandible : - the usual sequence is 3 4 5 7 . - the canines is lag behind 4 in early development and lies near inferior border of mandible , later it moves rapidly and pass 4 before it pierce gingival . - eruption of 3 might be blocked by D or causes its exfoliation . 4 usually erupts without causing any troubles . - rotation of premolars may occur due to uneven resorption of 1ry molars. Maxillary : -Usual sequence is 4 5 3 7 or 4 3 5 7 - upper 4 erupts following lower 3 or 4 . - upper canine has a torsous course : at 3 yrs , it lies high in maxilla , at level of floor of nose and its crown is directed mesially and lingually . -it uprights itself as it move toward occ plane , till it seems to hit distal aspect of lateral incisor root . -Deflected In a more vertical position , and erupts in a marked mesial inclination and high in alveolar process . -1st and 2nd premolars usually erupt in sufficient room as their MD diameter is less D,E leaving space to canines . -eruption of 7 ahead of 3 might lead to arch deficiency . Leeway Space : -Difference in M-D width between primary canine / molars and permanent canine/premolars . E-space : -If anterior crowding is present , send to orthodontist before primary 2nd molars exfoliate ( E-space ). Variation from ideal development in stage 2 :  Variation in spacing / crowding conditions : -Crowding in this region affect the last eruptive tooth either 3 or 5 . -When 5 is affected .it erupts palataly or lingually . in case of 3 , it erupts in labial side . impaction of 3 or 5 might be seen .  Variation in antero-posterior relationship : - Class 2 or class 3.  Variation in vertical relationships : - Rare , tongue  posterior open bite .
  • 10.   Variation in lateral relationships : -Crossbite Localized variation in tooth position : -Usually affect canines , due to its long path . it may be ectopically erupted in place of 2 or 4. -Stage 3 :    1- Third molar development : - Upper developed high with distal inclination and characterized by its long path of eruption . - Lower developed upright inclined with short vertical path. - Erupt in same relation as 1st and 2nd molars. Deviation in its position : a) Due to crowding : as it is the last tooth to erupt , impaction of 8 between 7 and ramus is a common feature . Upper could erupt in a crowded areas , but laterally or posterior . b) Due to developmental malposition : crowding Role of 3rd molar in late crowding ……